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 Post subject: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Sun 20, 2019 11:03 pm 
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Location: Farmington, New Mexico
Howdy!

I chronicled the restoration of my grandparent's DuMont television here several years ago. The digital to analog converter had failed a while back, and I recently purchased another. Trying to get everything working again today, the picture tube "quit". No picture. Yikes! There's not too many of those around.

Anyhoo, here's what I found: The adhesive that holds the bakelite tube base on the picture tube neck had failed. Thus, over time, apparently all the wires from the glass tube neck had disconnected from the bakelite tube base with the connector pins on it....I'm currently trying to re-attach the tube base and re-solder the wires to the pins on the bakelite tube base.

I'll let you all know how it goes. :shock: :shock:

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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Sun 20, 2019 11:28 pm 
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Well, crud.

That didn't work. I have sound, but no picture.

The filament in the neck of the picture tube is glowing, but the screen is dark. Unless I can figure something out, it would appear the DuMont is dead until I find another picture tube.

It was working earlier today. I have no clue what could have happened. The resoldering of the tube's wires to the pins looked to go smoothly.

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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 12:46 am 
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Joined: Jul Sun 13, 2008 4:02 pm
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Location: Scranton, PA 18505
I know this is going to sound dumb but I assume you checked to see if you still HV at the P2 button!


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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 2:31 am 
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I assume that you are sure that the wires all got inserted back into the correct pins all the way and are not folded over inside the base.

It is possible that the wires are not soldered securely inside the pins. Did you clean and tin the wires with new solder before you reinserted them into the pins? You can try reflowing the solder on the pins other than the filament.

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"One of the advantages of being disorderly is that one is constantly making exciting discoveries." A. A. Milne


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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 3:26 am 
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Location: Farmington, New Mexico
Howdy all!

Thanks for the suggestions and tips.

Not looking good. I have no idea how I did it, but it appears I wrecked the tube somehow....or it was just it's time to go?

Tim, I did make sure the wires went into the pins....I had cleared the solder from the pins prior to positioning the base back on the tube neck, and I could see them flush with the ends of the pins prior to soldering. No wires were missing from the pins. The wires were in the positions they were in when the came out...nothing crossed I've been soldering and resoldering for a while and for whatever reason it just isn't working. The CRT remains dark.

The filament is still glowing, and has been all along.

Ralph, I'm not sure what the P3 button is, but I do have high voltage at the metal cone of the tube. I swapped out the 1x2 tubes just to be sure.

I"m at a loss. I have an "old time" TV diagnosis/repair book and for the circumstances I have, it does say the issue is related to the high voltage section...but that is working as far as I can tell.

I've checked and double checked the connections at the plug that goes onto the tube...all seems well there.

I don't have a CRT tester. Does anyone know if there is a way to check a 19AP4 with a multi-tester/ohm meter, at least to see if the circuit has failed inside?

The CRT was working great just hours ago. Bright as always. It's really a bummer it seems to have failed.

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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 4:15 am 
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Location: WI 54812
Is it possible you bumped the ion trap out of it's proper position?


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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 4:31 am 
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Could you have accidentally moved the ion trap while working on the base? If you moved it then you will have to readjust it.

Edit: Posting at the same time as Kevin Kuehn.

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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 12:30 pm 
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Location: Farmington, New Mexico
Thanks for the tips and suggestions, folks!

I did check the ion trap, as it is pretty easy to accidentally move it. Unfortunately, it had no effect.

One issue with this set is that I never had the proper connector for CRT...or maybe only have part of it. The plastic/bakelite housing over the board has always been missing, so there's no stress relief on the solder joints. When our cat was smaller, he would get up there and knock stuff around, and every time I had to make any adjustments in the set, I would knock those wires around too, so they always had an issue with coming off the connector.

Now, after sleeping on it, I see I'm going to have to start a more methodical diagnosis process. :D I'm hoping that rather than the CRT being a goner, that perhaps when the last wire came off the connector, it touched something and took out something in that circuit. When that wire came off, the tube went dark, and it's never come back after that. The whole thing with the base coming off the tube happened after that, and might have nothing (fingers crossed!!) to do with the issue.

Incidentally, the red stuff between the black tube base and the neck of the tube is fingernail polish...I'd read that clear fingernail polish made a good glue to re-attach bases. My wife doesn't know where her clear fingernail polish is...so red it is! :lol: I made sure to keep it off everything but the tube base and glass (mostly I painted it onto the old glue, which is gobbed there quit heavy), because it occurred to me that the coloring in the polish could be metal flake and conduct electricity.

I'm going to have to dig out the Sams I purchased when I first restored the set. Hopefully I put it in the file with the rest of my schematics..this was pretty early in my restoration days and I didn't have the file then.

However, it might be a few days before I can get back to this set...my wife and I are taking our RV out to Navajo Lake State Park for a few days to get some fishing in before the weather starts turning really cold. We've already had a few nights below freezing, but Tuesday and Wednesday are supposed to be very nice..sunny and in the high 60's.


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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Mon 21, 2019 11:59 pm 
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Location: Beaver Falls, PA. USA
At this point, I would try to borrow a CRT tester to see if the tube is good. If you can dig up the schematic, see if the voltages on the CRT are correct.

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 Post subject: Re: Yikes! Bakelite end came off picture tube!
PostPosted: Oct Wed 23, 2019 1:54 am 
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Location: Lincoln City, OR 97367
Greetings to CaryLee and the Forum:

I see that Tim beat me to it. I suggest that you check the voltages on the various picture tube elements. Even if you can't find a schematic for your particular set, you should be able to find one with a similar tube; the voltages will be the same. I just fixed a problem with an HP 141T spectrum analyzer display by exactly this method.... systematically measuring all the voltages on the various tube element connections. I found 130 volts on a storage mesh that was only supposed to be 9 volts. Replacing a shorted diode got my display back. You may find something similar.

Good Luck,

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